5.1 audio only works after casting other 5.1 content

I have had this issue since launch and have already posted this on the big 5.1 audio thread here but I believe it be a different issue than 5.1 audio that doesn't work at all.

My Chromecast Ultra is connected to my Onkyo TX-NR686 receiver which is connected to a 5.1 speaker setup and a LG B8 TV. Every time I load up Stadia after shutting it down, my receiver shows to be receiving only a 2.0 stereo signal from the Chromecast, even after starting a game and playing a bit. My connection at all times shows Excellent and 5.1.

This is what I have to do to resolve it (every time):

Pause the game

Cast a 5.1 audio/video content source from my phone to the Chromecast(for example, a Netflix show) which shuts down Stadia to bring the other content up.

Load Stadia and go into the game again

Now Stadia is properly sending a 5.1 audio signal which I can see by an indication on my receiver.

I'll emphasize that it's not just a signal indication - I can verify hearing stereo sound before and 5.1 sound after coming from my speakers.

Is this a known problem? Is there a planned fix?We're getting closer to two months since launch and there hasn't seemed to be any update to the founder's edition Chromecast Ultra firmware. Why are updates so slow with so many reported issues?